The proposed studies are designed to examine the mechanisms associated with the biosynthesis of luteinizing hormone (LH) in the pituitary gland. This involves the assessment of individual LH subunit mRNA amounts, and how these amounts are regulated during the estrous cycle and by gonadotropin releasing hormone (GnRH). To address these questions, the following specific aims are proposed. First, it is planned to establish LH subunit mRNA amounts during the normal estrous cycle in the ewe. These times will be selected so that distinct phases of cycle (i.e. luteal, follicular, preovulatory surge) are represented, and as such, results can be interpreted relative to normal physiological states. Second, it is planned to assess the effect of GnRH on LH subunit mRNA amounts during times that represent these different physiological states. The studies will employ an animal model whose hypothalamus is hormonally "disconnected" from the pituitary gland and then pulsed with GnRH at frequencies that simulate phases of the normal cycle. Efforts will be concentrated on the time when pulse patterns change most dramatically (luteolysis through the preovulatory phase). Specific cDNAs will be used in hybridization assays to quantitate the alpha and LH beta mRNA levels in the pituitary tissue from these animals. The results will then be correlated with pituitary and serum LH amounts. By using these molecular biology approaches with a well-defined, in vivo, animal model system, mechanisms involved in LH biosynthesis, and its regulation, can be investigated. This will provide new information relative to the synthesis and regulation of this hormone.